In known metal anodes, especially dimensionally stable anodes, an active coat is applied to a row of horizontal circular titanium rods arranged parallel to one another, which rods are held together by means of uncoated transverse ribs. However, electrodes with round grid rods are unsatisfactory for several reasons, especially because of the disadvantageous current distribution resulting from "current shadow formation" with respect to the counter-electrode, at least in mercury electrolysis cells, and a remedy has been sought.
Metal anodes are also known in which electrical conductors distribute current over several planes in the electrode (compare, German Published Application (DE-AS) No. 1,818,035). Since, however, the conductor plane facing the counter-electrode consists of activated screen material, this has, as in the case of round rods, the disadvantage that relatively large active surfaces lie in the current shadow and the actual surface to be reached is relatively small with respect to the projected surface.
It has also been proposed to arrange the anode grid structure in the form of flat strips or bands or U-shaped channels or inverted U-channels, the latter of which is the subject of British Pat. No. 1,394,026. The individual channel-shaped parts are welded together at the connecting arcs of the inverted U-sections. The British patent provides for an adequate gap between the bands of each channel-shaped element to allow the access of a spot-welding tool-head when the channel-shaped elements are to be connected to a conductor by spot-welding. On the other hand, this limits the number of individual conductor elements, which should be high with regard to the current distribution. In addition, the arcs between the connecting cross-pieces at the top of the inverted U-elements must be removed, which results in relatively significant waste of titanium. Also, the problem of mass transfer, especially in mercury cells, is not solved.
It is the object of the disclosure of German Published Application (DE-AS) No. 2,323,497, to promote mass transfer, particularly for improved gas escape from the bottom of anodes in cells which operate with current densities greater than 10 kA/m.sup.2. The promotion of mass transfer is achieved by use of an exceedingly large active surface in the zones near, as well as far from, the counter-electrode. One drawback, however, is that the current transport occurs practically only over one conductor plane with a single transversely extending rod, which leads to a strongly variable current distribution at the active electrode surface.
A more significant drawback is that the main current distributor lies directly above the activated surface, so that the gas escape conditions and the flow conditions are not uniform at the active surfaces and are thus negatively influenced. The great height of the vertically arranged coated titanium bands result in their operating only slightly in the remote zone due to the relatively high electrolyte resistance, except at the cost of a higher voltage with a corresponding higher consumption of electrical energy, hence higher operating costs. As the bands are only inter-connected at the top by a few transverse welding seams, the bands of this electrode structure can very easily be brought apart at their outer ends, transversely to their longitudinal direction. The bands of this structure can moreover only be welded with great effort to the transverse beams.
German Published Application No. 2,323,497 does not address the problem of nevertheless ensuring adequate mechanical stability or form stability when using thin bands, especially with regard to bending and twisting stiffness. These requirements must be met, as must be the requirements of uniform current distribution, good gas kinetics, low fabrication and low repair costs, long life of the structure and coating, and good resistance to short-circuiting. The weight of the electrodes is likewise important, not only because of the manufacturing and transportation costs but also because of the expensive cost of the materials used.